Gas turbines typically include a compressor, a plurality of combustors, and a turbine section. The compressor pressurizes air flowing into the turbine. The pressurized air discharged from the compressor flows into the combustors. Air entering each combustor is mixed with fuel and combusted. Hot combustion gases flow from each combustor through a transition piece to the turbine section of the gas turbine to drive the turbine and generate power.
A typical compressor for a gas turbine may be configured as a multi-stage axial compressor and may include both rotating and stationary components. A shaft drives a central rotor drum or wheel, which has a number of annular rotors. Rotor stages of the compressor rotate between a similar number of stationary stator stages, with each rotor stage including a plurality of rotor blades secured to the rotor wheel and each stator stage including a plurality of stator vanes secured to an outer casing of the compressor. During operation, airflow passes through the compressor stages and is sequentially compressed, with each succeeding downstream stage increasing the pressure until the air is discharged from the compressor outlet at a maximum pressure.
In order to improve the performance of a compressor, one or more of the stator stages may include variable stator vanes configured to be rotated about their longitudinal or radial axes. Such variable stator vanes generally permit compressor efficiency and operability to be enhanced by controlling the amount of air flowing into and through the compressor by rotating the angle at which the stator vanes are oriented relative to the flow of air. Rotation of the variable stator vanes is generally accomplished by attaching a lever arm to each stator vane and joining each of the levers to a unison or synchronizing ring disposed substantially concentric with respect to the compressor casing. The synchronizing ring, in turn, is coupled to an actuator configured to rotate the ring about the central axis of the compressor. As the synchronizing ring is rotated by the actuator, the lever arms are correspondingly rotated, thereby causing each stator vane to rotate about its radial or longitudinal axis.
Current synchronizing ring and lever arm assemblies generally configure the lever arms to have a sliding engagement with the synchronizing ring at the rotational interface between such components. In particular, the lever arm is typically configured to slide radially and/or circumferentially at the rotational interface between the lever arm and the synchronizing ring as the ring is rotated. This sliding engagement generally produces excessive wear on the assembly components disposed at this sliding interface. Moreover, the sliding engagement utilized in conventional assemblies often provides inadequate support for the synchronizing ring. In particular, due to the relative sliding occurring between the lever arms and the synchronizing ring during rotation of the ring, the lever arms disposed at the top of the synchronizing ring typically do not support any of the ring weight. Accordingly, the lever arms disposed around the bottom of the synchronizing ring must support the full weight of the ring. Such inadequate support can lead to even further wear of the components disposed at the attachment interfaces between the lever arms and the synchronizing ring. Further, inadequate support may also result in excessive wear on the rub blocks circumferentially spaced around compressor casing, as the rub blocks must be utilized to support a portion of the ring weight.
Accordingly, a variable vane assembly that provides enhanced support for the synchronizing ring and also reduces the occurrence of wear would be welcomed in the technology.